In the modern telecommunications industry, standard communications systems are linked to each other using protocols based on the Open Systems Interconnection (hereinafter referred to as “OSI”) model. The goal of OSI is to create an open system networking environment where any vendor's computer system, connected to any network, can freely share data with any other computer system on that network. In fact, the OSI model would allow any terminal connected to any computer to access any application on any other computer provided that the computers were connected by some form of common network. In networks adopting the OSI reference model, data flow between systems is performed through the OSI environment. The OSI model for network communications defines seven layers, each of which performs specific communications operations independent of the other layers. The seven layers are divided largely into upper layers and lower layers. The upper application-oriented layers perform services related to session management, data abstraction, and applications. The upper layers provide services that handle the applications, and the structuring, and encoding of data. The lower, network-dependent, layers provide services related to the physical connections, types of links, and routing functions. The lower layers provide transparent connections over diverse network configurations and a consistent interface to the upper layers.
The upper layers comprise an application layer, a presentation layer, and a session layer. The application layer executes protocols for user and network operation management and enables communications between the users' CPUs (central processing units). This layer provides services to the user and applications, such as job control, file transfer facilities, electronic mail, virtual terminal and directory services. The presentation layer has structure for communication between function modules of the application layer and handles presentation formats of information. This layer negotiates a common syntax used to encode data for data transfer and allows data to be transferred, independent of hardware considerations. The session layer controls dialog between the application layers. This layer provides organizing functions for synchronizing dialog and session recovery from lower layer problems.
The lower layers comprise a transport layer, a network layer, a data link layer, and a physical layer. The transport layer enables correct communications between terminals even if the upper layers do not consider the quality of line or physical constitution of additional systems. This layer provides an interface between the upper layers and the lower layers, concealing the detailed functional operation of the physical network connections to provide a network-independent service to the application-oriented upper layers. The network layer provides data transfer services. This layer provides addressing and routing functions, and may also include flow control between networks. The data link layer transmits data correctly without a hitch by enhancing reliability of a physical link in a logic network. This layer takes the information provided by the physical layer and adds error detection and retransmission functions. At this stage data is treated as units of data. The physical layer defines a physical interface between physical media, and transmits and receives bits according to the transmission requirement from the data link layer.
In an open system, user program data in a system A is entered into OSI environment and the data is transferred from the application layer to the physical layer in sequence to transmission media. Here, the data is enclosed in frames used in a high-level data link control (hereinafter referred to as “HDLC”) procedure prior to transmission. The frame passes a data switching network, so-called a relay open system in the OSI model, and arrives at a receiving computer in the open system. In the receiving computer, the data is passed from the physical layer to the application layer in sequence and, finally, transmitted to an application process B, the destination in a system B in the open system.
The data flow between systems may be performed between systems or a system and a terminal connected to another system. However, communications between more than two systems with different protocols is restricted. Thus, a protocol converter is required to perform data communications between different communication networks.
As a prior art, U.S. Pat. No. 5,852,660, Lindquist et al., discloses a network protocol conversion module within a telecommunications system. The U.S. patent provides a method and apparatus for enabling telecommunications signals containing application layer data generated by a first SS7 (Signaling System No. 7) telecommunications network to be transported across a second SS7 telecommunications network, wherein the first SS7 telecommunications network and the second SS7 telecommunications network are incompatible.
Conventional protocol converters allow two different protocols to exchange data between CPUs. It means direct data exchange between applications, or data exchange using simple logic between devices. In those conventional protocol converters, time delay is generated while the CPU performs other tasks. In addition, while one CPU receives signals and exchanges responses with the inside of system, a load on the CPUs and a waste of time are caused thereby incurring a large loss in the view of performance.
Conventional protocol conversion methods for communications between various network protocols are classified into three classes.
First, there is 1 to 1 protocol conversion method. This method converts a particular layer of a particular protocol into a corresponding layer of another protocol, based on the seven-layered OSI model. In order to convert m layers, m conversion methods are required and in order to convert n protocols, nC2 methods are required. As a result, m□nC2 methods are required in total. Therefore, for data exchange between various network protocols having various protocol layers, a lot of conversion methods are required thereby causing great complexity.
Second, there is a method of converting into a particular protocol. This means to convert n network protocols into a particular network protocol selected from the n network protocols. In order to convert n network protocols into a particular protocol, (n−1) conversion methods are required and in order to convert m layers, m conversion methods are required for each protocol. As a result, m□ (n−1) methods are required in total. Although it shows less complexity in converting network protocols compared to the first method, it still requires a lot of protocol conversions.
Third, there is a method of utilizing an overlay way. For example, it is IP-over-IEEE1394, IP-over-ATM, and so on. These are structures that an internet protocol, IP, is laid on an IEEE1394 or ATM layer. They do not perform particular conversions and are not data exchange methods between different network protocols. In other words, in the IP-over-IEEE1394, an apparatus in an IEEE1394 network transmits IEEE1394 data laid on the IP and receives data through the IP. The data received through the IP is passed through the IEEE1394 layer so that the IEEE1394 apparatus can accept the data. Therefore, it is not data exchange between different network protocols.
For example, U.S. Pat. No. 5,715,250, Watanabe, discloses an ATM-LAN (asynchronous transfer mode local area network) connection apparatus capable of connecting terminals of different protocol standards. The U.S. patent provides a small-scale ATM-LAN connection apparatus which enables communications between first and second ATM terminals of different standards, namely, the first ATM terminal of a LAN emulation protocol and the second ATM terminal of an IP over ATM protocol.
However, the above-mentioned conventional protocol conversion methods have problems such as complexity in conversion methods, complexity due to different layer architectures and roles of protocols, and complexity in accessing apparatuses in different networks. In other words, the number of conversion methods increases in proportion to the number of network protocols to be converted and the number of layers in the network protocols to be converted, thereby increasing complexity. In addition, when the protocol conversion is performed, the complexity increases by times of a particular factor, because the protocol layer architectures and roles of each layer in each network protocol are very different based on the seven-layered OSI model. The particular factor may depend on the number of option fields and tasks to be treated in each protocol layer. Moreover, there is no common address hierarchy recognizable between different network apparatuses when communications between the different network apparatuses are performed.